The present invention relates to in general to an optical disk system, and more particularly, to a track cross signal correction apparatus for seeking tracks in an optical disk system.
In general, an optical disk system seeks tracks in order to find a desired track. Both direct and indirect seek methods are used to locate a track. In such methods, a track cross signal is counted to perform a more efficient direct seek. The optical disk system utilizes a tracking error signal as shown in FIG. 2A, which is obtained from a beam reflected from a disk for a tracking control operation. The tracking error signal is obtained from an optical beam crossing the tracks on the disk, and is compared with a predetermined level to obtain a track cross signal as shown in FIG. 2B. The track cross signal represents the number of tracks on the disk that have been traversed.
Meanwhile, when signal recording surfaces of the disk are contaminated with foreign matter and/or the disk is swayed during rotation, the intensity of the beam reflected from the disk is lowered, thereby distorting the waveform of the tracking error signal as shown by "a" in FIG. 2A. If the waveform of the tracking error signal is distorted, the track cross signal becomes inaccurate. Thus, the track cross signal must be corrected before it is counted.
FIG. 1 shows a conventional track cross signal correction apparatus in a general magneto-optical disk system. When first and second counters 11 and 15 receive a track cross signal, the counters 11 and 15 count the number of reference clock pulses with respect to a high-level pulse T1 of the track cross signal, and outputs the count values representing the width of the pulse T1 of the track cross signal, as shown in FIG. 2B. The first counter 11 outputs the count value to a shift register 13 and an adder 17. The second counter 15 outputs the count value to a comparator 19. The shift register 13 shifts the binary count value by one bit to the right to generate and output half the count value. The adder 17 adds the output value of the first counter 11 and the output value of the shift register 13, and outputs a count value C representing one and a half the width of the pulse T1. The count value C becomes a reference value for judging whether a pulse is missing at a point where the pulse should exist. During the time when the reference count value C is generated via the shift register 13 and the adder 17, the counters 11 and 15 perform a count operation with respect to a next high-level pulse T2. The second counter 15 and the adder 17 output the respective output values to the comparator 19. The comparator 19 compares the reference count value C output from the adder 17 with the count value D output from the second counter 15. As a result, if C&lt;D, that is, the next pulse is not generated during the time corresponding to one and a half of the previous pulse width T1, it is determined that the pulse following the pulse T1 is missing. In this case, the comparator 19 generates a control signal to insert the missing pulse thereinto.
In cases when a track seek operation is performed in an optical disk, such as a compact disk (CD) using the FIG. 1 apparatus, noise components and glitches tend to occur and concentrate at the zero crossing portion of a tracking error signal (as shown in FIG. 3A), due to a scattering beam being reflected when the optical beam passes through an edge portion of the pit and because of electrical noise resulting. The glitches are indicated by "b" in FIG. 3A. If a track cross signal is generated because of the tracking error signal, the glitch will still exist in the track cross signal as shown by "c" in FIG. 3B. The apparatus illustrated in FIG. 1 does not remove the glitches which exist at the edge of the track cross signal. Thus, since the glitch is incorrectly counted as a track cross pulse, an accurate track seek operation cannot be accomplished.